This invention relates in general to vehicle braking systems, and in particular to an electrically actuated hydraulic power cylinder for use in advanced vehicle braking systems
Electric motors are convenient and well known devices for converting electrical power into motion. The rotary motion produced by electric motors can be converted into a linear motion, which is more useful in certain situations, in a number of ways. One actuator device which is known for converting rotary motion into linear motion is the spindle gear mechanism disclosed in U.S. Pat. No. 4,926,708 to Dietrich et al., the disclosure of which is incorporated by reference herein.
Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are actuated when an operator of the vehicle depresses a brake pedal. Typically, the brake pedal is mechanically linked to a master cylinder of a hydraulic brake system. When the brake pedal is depressed, the master cylinder is operated to pressurize a volume of hydraulic fluid, and direct the pressurized hydraulic fluid via hydraulic brake lines to the brake assemblies at the wheel.
In order to increase the force with which the brake assemblies are applied, while keeping the force that the driver has to apply to a brake pedal at a reasonable value, various pneumatic or hydraulic booster mechanism have been developed to assist the driver in applying a force to the master cylinder.
More recently, the industry has been developing brake systems in which the brake pedal is not normally hydraulically connected to the brake assemblies. The driver does not supply any portion of the force actuating the brake assemblies. Instead, sensors are actuated when the brake pedal is depressed. These sensors generate a signal indicative of a desired amount of braking being demanded by the driver. This signal is input to a controller which controls operation of a electromechanical mechanisms which supply the force needed to actuate the brake assemblies. These electromechanical mechanism typically include an electrical motor driven pump supplying high pressure brake fluid to the brake assemblies through an arrangement of valves which are operated to regulate the pressure of the brake fluid supplied to the brake assemblies based upon the driver's brake demand signal. The driver's brake demand signal may be modified by the controller to accomplish such "intelligent" braking schemes as Antilock Braking (ABS), Traction Control (TC), Vehicle Stability Control (VSC), and Collision Avoidance (CA).